The factors influencing the enrichment of organic matters in the Carboniferous source rocks, Ounan depression, eastern Qaidam basin
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摘要:
柴达木盆地东部地区欧南凹陷是石炭系油气运聚成藏的有利构造单元,具有一定勘探潜力,但对有机质富集机理认识不清导致对优质烃源岩分布的预测缺乏有效指导,制约了油气勘探进程。基于地球化学分析、XRD、SEM等分析测试,对石炭系烃源岩矿物组分、有机质丰度、干酪根类型、热演化程度、形成环境、TOC与主要矿物关系等进行了综合研究,明确了有机质富集的主要影响因素。结果表明:石炭系发育大量“差—中等”级别和少量“好”以上级别泥页岩和碳酸盐岩烃源岩,形成于咸水、干热、弱还原—弱氧化过渡带的海陆交互陆棚沉积环境;分散有机质由海相和陆相混源型生物有机质组成,整体处于“成熟—高成熟阶段”,烃源岩主要残留Ⅲ型干酪根,但抽提的氯仿沥青“A”主要来自于Ⅱ型干酪根;高丰度烃源岩TOC随石英矿物组分增大而升高,富含硅质微体生物化石,高硅烃源岩中硅质证实为生物成因,推测石炭纪硅质生物的参与引起海相生物有机质的富集并极大提高了沉积物初级生产力。研究认识为研究区石炭系优质烃源岩分布预测和下一步油气资源部署提供了依据。
Abstract:The Ounan depression is a favorable structural unit for the Carboniferous hydrocarbon migration and accumulation, which demonstrates certain exploration potential. However, the organic matter enrichment mechanism is still unclear, which results in the absence of effective guidance for predicting the distribution of high-quality source rocks and restricts the process of oil and gas exploration. Based on geochemical analysis and XRD, SEM and other tests, the main factors influencing the enrichment of organic matters in Carboniferous source rocks have been identified through a comprehensive investigation into the aspects such as mineral composition, organic matter abundance, kerogen type, thermal evolution degree, formation environment, and the relationship between TOC and primary minerals. The results reveal that shales and carbonate source rocks have been developed in the Carboniferous, a large quantity at poor-medium level and a few at good or above level. They were deposited in the environment of intercontinental shelf with saline-water, arid-hot climate and weak oxidation and reduction. The dispersed organic matters are composed of mixed marine and terrestrial origins, which are overall in a "maturity-high maturity stage". The Carboniferous clastic source rocks are mainly residual type Ⅲ kerogen, but the extracted chloroform bitumen "A" is mainly derived from type Ⅱ kerogen.TOC values increase with the growing of quartz minerals because the high-abundance source rocks are rich in siliceous biological fossils. The SiO2 in the high-SiO2 source rocks has been identified as biogenic, suggesting that the participation of siliceous organisms in the Carboniferous cause the enrichment of marine organic matters and greatly improve the primary productivity of the sediments. This study provide the basis for predicting the distribution of Carboniferous high-quality source rocks and the deployment of oil and gas resources in the study area.
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Key words:
- biogenic silica /
- organic enrichment /
- high-quality source rock /
- Carboniferous /
- Ounan depression /
- Qaidam basin
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图 2 柴东地区南北向地质剖面(AB位置见图 1b)
Figure 2.
图 9 石炭系烃源岩埋深-RO剖面(QDD1井RO数据来源于刘奎等(2020))
Figure 9.
表 1 欧南凹陷及周边野外露头和重点钻井石炭系烃源岩样品矿物组分
Table 1. Whole rock mineral compositions of the Carboniferous source rocks by XRD analysis, Ounan depression
序号 样品编号 取样点 岩性 层位 深度/
mXRD全岩矿物组成/% 石英 钾长石 斜长石 方解石 白云石 菱铁矿 黄铁矿 黏土矿物 1 SHG-1 石灰沟 泥岩 C1h — 30.3 — — — — — — 69.7 2 SHG-2 灰岩 C1h — 24.1 — — 51.4 — — — 24.5 3 SHG-3 泥岩 C2k — 40.4 — 1.9 — — — — 57.7 4 SHG-4 页岩 C2k — 16.4 — — — — — — 83.6 5 WGX-1 旺尕秀 页岩 C2k — 44.0 — — — — — — 56.0 6 WGX-2 页岩 C2k — 51.9 — — — — — — 48.1 7 BSG-1 柏树沟 页岩 C2zh — 57.0 — — — — — — 43.0 8 BSG-2 页岩 C2zh — 42.0 — — 54.5 — — — 3.5 9 BSG-3 泥岩 C2zh — 34.2 — — — — — 18.2 47.6 10 BSG-4 灰岩 C2zh — 5.1 — — 94.4 — — — 0.5 11 BSG-5 灰岩 C2k — 3.9 — — 96.0 — — — 0.1 12 BSG-6 灰岩 C2k — 10.2 — — 89.3 — — — 0.5 13 BSG-7 灰岩 C2k — 23.9 — 2.2 52.5 8.3 — — 13.1 14 BSG-8 灰岩 C2zh — 0.8 — — 99.0 — — — 0.2 15 QDC-1 QDC1 泥岩 C2k 3393.80 71.9 — — 2.1 — — — 26.0 16 QDC-2 灰岩 C2k 3395.20 6.0 — — 88.1 4.8 — — 1.1 17 QDC-3 灰岩 C2k 3395.50 20.6 — — 59.1 6.8 — 1.6 11.9 18 QDC-4 泥岩 C2k 3398.80 34.6 — — 21.8 4.3 — 2.8 36.5 19 QDC-5 泥岩 C2k 3400.10 38.2 — — 4.2 2.4 — 2.6 52.6 20 QDC-6 泥岩 C2k 3401.40 35.6 — — — — — 2.6 61.8 21 CY2-1 CY2 泥岩 C2k 657.43 67.4 — — — 8.9 — — 23.7 22 CY2-2 泥岩 C2k 923.90 48.2 — — 16.2 18.2 — — 17.4 23 CY2-3 泥岩 C2k 950.20 50.6 — 2.2 — — 15.6 — 31.6 24 CY2-4 灰岩 C2k 958.50 19.3 — — 21.3 16.1 28.1 — 15.2 25 CY2-5 灰岩 C2k 992.30 7.3 — — 90.5 2.0 — — 0.2 26 CY2-6 泥岩 C2k 1010.40 88.3 — — — 2.7 — — 9.0 27 CY2-7 灰岩 C2k 1031.70 4.4 — — 95.3 — — — 0.3 28 CY2-8 泥岩 C2k 1042.30 45.1 — 2.3 1.7 — — — 50.9 29 CY2-9 灰岩 C1h 2381.40 11.9 2.2 — 35.0 15.3 — — 35.6 30 CY2-10 灰岩 C1h 2388.60 9.2 0.8 — 79.0 — — — 11.0 31 CY2-11 灰岩 C1h 2400.30 1.9 — — 88.6 9.0 — — 0.5 均值 泥页岩 46.8 — 0.3 5.2 1.8 0.9 1.3 42.3 均值 灰岩 10.6 0.2 0.2 74.3 4.5 2.0 0.1 8.2 表 2 欧南凹陷及周边石炭系烃源岩样品有机地化特征和黏土矿物组分
Table 2. Organic geochemistry characteristics and clay mineral compositions of the Carboniferous source rock samples, Ounan depression
序号 样品编号 岩性 烃源岩测试/% 黏土矿物在全岩中的相对含量/% TOC 氯仿沥青“A” RO 伊/蒙混层 伊利石 高岭石 绿泥石 I/S比 1 SHG-1 泥岩 7.44 0.1900 — 10.46 4.88 54.37 — 25 2 SHG-2 灰岩 0.57 0.0900 1.44 7.35 2.45 14.70 — 25 3 SHG-3 泥岩 12.96 0.5200 — 17.31 3.46 36.93 — 35 4 SHG-4 页岩 6.55 0.1600 — 23.41 9.20 51.00 — 20 5 WGX-1 页岩 17.21 — 1.08 25.76 14.56 15.68 — 25 6 WGX-2 页岩 21.17 — — 12.03 6.25 29.82 — 20 7 BSG-1 页岩 22.73 0.0093 1.36 13.33 6.02 23.65 — 25 8 BSG-2 页岩 0.96 0.0027 1.24 3.50 — — — — 9 BSG-3 泥岩 14.51 0.0142 1.63 23.80 8.09 15.71 — 25 10 BSG-4 灰岩 0.66 0.0014 1.47 0.50 — — — — 11 BSG-5 灰岩 0.09 — — 0.10 — — — — 12 BSG-6 灰岩 0.15 — — 0.50 — — — — 13 BSG-7 灰岩 1.29 — — 5.24 2.75 5.11 — 20 14 BSG-8 灰岩 0.17 — 1.30 0.20 — — — — 15 QDC-1 泥岩 3.00 — 2.55 — — — 26.00 — 16 QDC-2 灰岩 1.45 — — 1.10 — — — — 17 QDC-3 灰岩 1.52 — — 5.36 3.93 1.31 1.31 20 18 QDC-4 泥岩 2.81 — — 15.33 13.51 4.38 3.29 20 19 QDC-5 泥岩 0.73 — — 21.57 18.41 6.31 6.31 20 20 QDC-6 泥岩 1.30 — 2.57 32.75 13.60 8.03 7.42 25 21 CY2-1 泥岩 2.53 — 1.30 7.58 6.64 5.93 3.56 25 22 CY2-2 泥岩 2.06 — 1.37 8.35 4.52 2.78 1.74 20 23 CY2-3 泥岩 16.52 — 1.46 13.27 8.53 9.80 — 20 24 CY2-4 灰岩 0.28 — — 5.02 3.04 7.14 — 15 25 CY2-5 灰岩 0.17 — 1.39 0.20 — — — — 26 CY2-6 泥岩 27.83 — — 3.24 2.70 1.53 1.53 15 27 CY2-7 灰岩 3.40 — 1.52 0.30 — — — — 28 CY2-8 泥岩 8.72 — — 18.32 12.73 13.74 6.11 20 29 CY2-9 灰岩 0.51 — — 5.34 23.14 — 7.12 10 30 CY2-10 灰岩 0.45 — 1.79 2.53 3.96 — 4.51 15 31 CY2-11 灰岩 0.39 — — 0.50 — — — — 均值 泥页岩 9.94 0.15 — 14.7 7.8 16.5 3.3 — 均值 灰岩 0.79 0.05 — 2.5 2.8 2.0 0.9 — -
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